Knowledge Bank

The pure rotational quasibound spectra of $HeH+$ and $HeD+$ have been observed in the mid infrared region using diode laser velocity modulation absorption spectroscopy. Four quasibound to quasibound $(Q-Q)$ and three bound to quasibound $(B-Q)$ transitions of $HeH+$ and one bound to quasibound transition of $HeD+$ have been detected in a low pressure ac glow discharge. The highest quasibound level involved in the spectra $(HeH+,v=0,J=26)$ is $2000cm-1$ above the dissociation limit. The measured transition frequencies are in very good agreement with ab intio calculations. Two of the $Q-Q$ transitions have wider linewidths due to lifetime broadening.